Binary Aqueous Solvent Research Articles

Chromophore end-labelled long chain perfluoropolyether as probes to study the formation of aggregates in aqueous organic solvent and their asymmetrical coaggregation with hydrocarbons

The emission spectra of 2-naphthyl and 9-anthryl ester terminated perfluoropolyether compounds (NpOF and AnOF) in aqueous organic binary solvents were investigated. The fluorescence spectra of NpOF in dimethyl sulfoxide–water mixture (DMSO–H2O) are dominated by the excimer emission. Addition of methyl perfluoropolyether carboxylate (CH3OF) to the solution results in a reduction in the excimer emission and an enhancement of monomer emission. Selective excitation of the naphthalene moiety in the mixture solution of NpOF and AnOF leads to strong emission from AnOF. All these observations suggest the formation of perfluoropolyether aggregates in the aqueous organic binary solvents.Both NpOF and dodecyl 2-naphthoate (NpHC12) in 1,4-dioxane–H2O exhibit the excimer emission exclusively. Addition of a high concentration of n-C18H38 to the NpOF solution results in a reduction in the excimer emission and an enhancement of monomer emission, suggesting that chromophores of NpOF are diluted by the C18H38 aggregates. Addition of a high concentration of CH3OF to the NpHC12 solution, however, has only slight effect on the fluorescence of NpHC12 emission. These observations indicate that when coaggregation of hydrocarbon and perfluoropolyether occurs, these coaggregates contain much more hydrocarbons than perfluoropolyether compounds.

Ternary complexes in gels from agarose and from chemically-modified agarose

Thermodynamic data and mechanical measurements are shown for gels prepared in aqueous binary solvents (water/DMSO, water/DMF, water/methyl formamide and water/formamide). When electrostatic interactions, as opposed to hydrogen bonding, can be established with the cosolvent (DMSO, DMF, methyl formamide) we come to the conclusion that ternary complexes are formed (agarose/water/cosolvent). In the case of chemically-modified agarose (OH groups replaced by OCH 3 groups) we suggest that these cosolvents are directly involved in the formation of the gel.

Preferential solvation studies using the solvatochromic dicyanobis(1,10-phenanthroline)iron(II) complex

Solvent effects on the electronic spectra of dicyanobis(1,10-phenanthroline)iron(II) have been investigated in thirteen pure solvents and twenty binary solvent mixtures. In pure solvents, the shifts of the νmax values are found to depend on more than one of the known solvent parameters (AN, α, β, DN and π*). AN, α and π* are found to be the most important solvent parameters, exerting a considerable effect on the solvatochromic shifts of the title complex. The preferential solvation of dicyanobis(1,10-phenanthroline)iron(II) in binary solvent mixtures has been investigated by monitoring the metal–ligand charge transfer band of the indicator complex. Organic solvents are preferred near the indicator complex in aqueous binary solvent mixtures (negative deviation), except in regions rich in MeCN, Me2CO and 1,4-dioxane, where water molecules are preferred over the organic component (dual behavior). However, the indicator complex is preferentially solvated by the component which has the higher acceptor number in non-aqueous binary solvent mixtures. Negative deviation was observed in binary mixtures of CHCl3 and Me2CO with alcohols and positive deviation in mixtures of CHCl3 with THF, DMSO and Me2CO. Different criteria were considered to evaluate the extent of preferential solvation in different solvent mixtures, iz., the local molar fraction (XAL), the excess function (ΔX), the iso-solvation point (XBiso) and the preferential solvation constant (KA/B). The preferential solvation data have been linearly correlated with the different solvent parameters.

Carbohydrates Exhibit a Distinct Preferential Solvation Pattern in Binary Aqueous Solvent Mixtures

Molecular dynamics simulations reveal the entire solvation shell around a model disaccharide dissolved in the binary 1:3 molar mixture of dimethyl sulfoxide and water becomes distinctly structured (see drawing). Such preferential solvation is due to the large number of hydroxyl groups and the rich network of hydrogen bonds of a disaccharide formed with the solvent.

Carbohydrates Exhibit a Distinct Preferential Solvation Pattern in Binary Aqueous Solvent Mixtures

Moleküldynamik-Simulationen zeigen, dass die gesamte Solvatationshülle um ein Modelldisaccharid, das in einem Gemisch aus Dimethylsulfoxid und Wasser (75 Mol-% Wasser) gelöst vorliegt, deutlich strukturiert ist (siehe Bild). Diese bevorzugte Solvatation ist auf die große Zahl an Hydroxygruppen und das ausgedehnte Netz aus Wasserstoffbrückenbindungen zwischen dem Disaccharid und dem Solvens zurückzuführen.

Kinetic solvent effect on the hydrolysis of N-Benzylbenzohydroxamic acid in some binary aqueous solvent mixtures

Abstract The rates of acidic hydrolysis of N-benzylbenzohydroxamic acid were measured over the temperature range 45–65°C in aqueous 1,4-dioxane, dimethylsulfoxide, N,N-dimethylformamide, tetrahydrofuran, sulfolane, acetone, and methanol of different composition [10–70% (v/v)]. The rate constant varies with the varying composition of solvent which is attributed to differential solvation of the transition state, solute solvent interactions, solvent structure, and dielectric behaviour of the medium. The solvatochromic parameters and linear solvation energy relationships ‘π” for the dipolarity/polarizability, ‘β’ for the hydrogen-bond accepting ability and ‘α’ for the hydrogen bond donating ability of solvent mixtures have been used through multiple regression of the rate constants. The activation parameters ΔH≠, ΔS≠, and ΔG≠ have also been evaluated.

Scleroglucan gel volume changes in dimethylsulphoxide/water and alkaline solutions are partly caused by polymer chain conformational transitions

The relative equilibrium volume, V/ V 0, of swollen scleroglucan gels was determined at temperatures T from 4 to 40°C in aqueous alkaline solutions and binary solvents containing water and dimethylsulphoxide (DMSO), respectively. In some of the experiments scleroglucan was crosslinked using sodium- meta-periodate. In others the crosslinks were Schiff bases between the polyaldehyde of scleroglucan and primary amines on small amounts of added chitosan. The V/ V 0 showed discontinuous changes at a water weight fraction W H=0.13, independent of the temperature from 4 to 40°C in DMSO/water solvents. The V/ V 0 of the gels decreased when the pH in aqueous solvents was raised above 13. Both these findings coincide with the known strand separation of the triple-helical structure occurring under these solvent conditions. An additional abrupt change in V/ V 0 occurred at W H=0.84 and T=20°C for the binary DMSO/water solvents. This transition was shifted towards lower W H for increasing temperatures, at T=40°C it occurred at W H=0.56, which is similar to the temperature effect of the intra-triple-helical conformational transition of scleroglucan. This study indicates that the conformational transitions of the elastically active chains of the polymer network can affect the equilibrium volume of swollen polymer gels.

Structure, solvatochromism, and solvation of trans-[Co-III(cyclam)(NCS)(2)](NCS) and the structure of [Co-II(Me(4)cyclam)(NCS)](2)[Co(NCS)(4)]MeOH

The structures of trans-[CoIII(cyclam)(NCS)2](NCS) and of [CoII(Me4cyclam)(NCS)]2[Co(NCS)4]·MeOH have been established by X-ray diffraction methods. The solvatochromic behavior of the trans-[Co(cyclam)(NCS)2]+ cation in several binary aqueous solvent mixtures is reported. Transfer chemical potentials for this complex from H2O into MeOH-H2O mixtures have been established from solubility measurements on its thiocyanate salt. The solvatochromic behavior of this cation is discussed in the context of other solvatochromic inorganic complexes; its transfer chemical potentials are discussed in relation to those of other cobalt(III) complexes.

The determination of crown-cation complexation behavior in dioxane/water mixtures by conductometric studies

Using conductance measurements, an attempt has been made to gain detailed information about the specific molecular interactions of crown compounds with metal ions in a 1,4-dioxane/water binary system. Analyses of the transport data of dioxane/water mixtures yielded the mobility of the crown compound action complexes and the ion-pair dissociation constant of the crown compound–electrolyte complex. Binary mixed aqueous solvents are frequently employed in broad areas of chemistry. Their applicability ranges from synthetic and mechanistic studies in organic chemistry to biophysical chemistry, with emphasis on molecular interactions in biologically significant structures. Stability constants of crown compound complexes are determined by various methods, such as potentiometry (with ion selective electrodes), polarography, voltammetry, spectrophotometry, nuclear magnetic resonance, calorimetry and solubility. In this study the conductometry measurements have been carried out with high precision at optimal concentrations in dioxane/water systems. Structures of crown–cation complexes in dioxane/water mixtures are estimated from the conductance parameters (κ, Λ and α) as well as the complex formation constant, Ke = (ΛMAm − Λ) / (Λ − ΛMaLbAm) [L]. The conductance behavior of Na+, K+ chlorides and Na+ perchlorates with 18-crown-6, 15-crown-5, and 12-crown-4 have been studied in various dioxane/water systems (50%, 80%, and 85%) at 25°C. The all experimental studies have been made by the ratio 1 : 1 of the metal-ion and the crown ether, Ke. For the calculations, Excel. 5.0 was used as an application program. Copyright © 1998 John Wiley & Sons, Ltd.

Structure−Properties Relation for Agarose Thermoreversible Gels in Binary Solvents

The structure of agarose gels prepared in aqueous binary solvents has been studied by means of X-ray and neutron small-angle scattering. The scattering curves are interpreted by considering a random assembly of straight fibers displaying cross-section polydispersity. The cross-section polydispersity is well accounted for with a distribution function of the type w(r) ∼ r-λ bounded by two radii, rmin and rmax, and where λ depends upon both the nature of the binary solvent and the agarose concentration. Departure from the Porod regime at wide scattering angles suggests the existence of free and/or dangling chains that do not participate in the network elasticity (loose chains). The fraction of loose chains gradually vanishes upon increasing the agarose concentration. Experimental elastic modulus−concentration relations obtained on the same type of samples point to the occurrence of entropic elasticity once analyzed in light of the existence of loose chains. Entropic elasticity is rather consistent with disor...

Oxidation of [Co(en)2(SOCH2CO2)]+ by S2O82− and by IO4− in binary aqueous solvent mixtures at pressures up to 1.25 kbar

Second order rate constants and activation parameters ΔH‡, ΔS‡, and ΔV‡ have been measured for the oxidation of [Co(en)2(SOCH2CO2)]+ by S2O82− and by IO4− in highly aqueous H2O – t-BuOH mixtures. The changes in solvation on going from the initial to the transition state are discussed on the basis of the transfer functions ΔGto, ΔHto and ΔSto. Whereas ΔGt‡ changes smoothly as the proportion of t-BuOH increases, the plots of ΔHt‡ and TΔSt‡ exhibit mirror behaviour and pass through extrema located around x2(t- BuOH)=0.038. Information on the role of solvation is complemented by the determination of activation volumes. These are discussed in terms of intrinsic and solvational contributions. It is proposed that changes in hydrophobic hydration are of principal importance in determining the response of ΔH‡, ΔS‡, and ΔV‡ to changes in solvent composition in H2O – t-BuOH mixtures.

Excited-State Intramolecular Proton Transfer of 2-(2‘-Hydroxyphenyl)benzimidazole in Cyclodextrins and Binary Solvent Mixtures

The excited-state intramolecular proton transfer (ESIPT) of 2-(2‘-hydroxyphenyl)benzimidazole (HBI) has been studied using absorbance, steady-state, and time-resolved emission spectroscopies in cyclodextrins (β-, γ-, and 2,6-di-O-methyl-β-cyclodextrins) and in binary aqueous solvent mixtures. The spectral characteristics of HBI in cyclodextrins and binary solvent mixtures (dioxane:water, MeOH:water, and solutions of cyclohexane containing MeOH and trifluoroethanol) are compared to further study the effects of various microenvironments on the ground and excited-state properties of the molecule. The intermolecular interactions of HBI with cyclodextrins and various solvents appear to weaken intramolecular hydrogen bonding in HBI and facilitate the formation of strong intermolecular hydrogen bonds with the various cyclodextrins and solvent molecules. The acquired data are used to suggest the formation of a zwitterionic structure of HBI in cyclodextrins.

Ternary complexes in agarose gels prepared from binary solvents

AbstractThe thermoreversible gelation of agarose has been investigated in four different aqueous binary solvents: Water/dimethyl sulfoxide, water/N,N‐dimethylformamide, water/N‐methylformamide, and water/formamide. The phase diagrams have been subsequently established as a function of agarose concentration and solvent composition. These diagrams suggest the formation of ternary complexes agarose/water/cosolvent.

Reactivity and solvatochromism of pentacyanoferrate(II) complexes in diol–water mixtures

Rate constants are reported for substitution at the pentacyanoferrate(II) ions [Fe(CN)5L]3−, where L=3,5-dimethylpyridine or 3-cyanopyridine, in binary aqueous mixed solvents containing up to 60vol% 1,2-ethanediol, 1,2-butanediol, methanol or ethanol. Trends for diol-containing mixtures are compared with those for monohydroxylic alcohols, and the reactivity pattern for these complexes is compared with those established earlier for base hydrolysis of tris(1,10-phenanthroline)iron(II) and for the aquation of cis-dichloro-bis- (1,2-ethanediamine)cobalt(III). The solvatochromic behaviour of several pentacyanoferrate(II) ions has been established in binary aqueous mixtures containing 1,2-ethanediol, 1,2-butanediol, 1,4-butanediol and 1,2-pentanediol. A correlation between reactivity and solvatochromism is presented.

Phase Behavior of Agarose in Binary Solvents

The thermoreversible gelation of agarose has been investigated in four different aqueous binary solvents: water/dimethyl sulfoxide, water/N,N-dimethylformamide, water/N-methylformamide, and water/formamide. The thermal behavior through the gelation/melting temperatures and the gelation/melting enthalpies has been studied, and phase diagrams have been subsequently established as a function of agarose concentration and solvent composition. The elastic modulus has been determined as a function of the same parameters. The results are discussed by considering different possible models. It is suggested that agarose/water/cosolvent ternary complexes can account for the experimental results.

Formation of Stable Gel Colors of Calcium Alginate

Abstract By a newly developed gel-preparation method using binary aqueous mixed solvents, such as a methanol–water or an ethanol–water mixture, before gelation as a sol solvent and after gelation as a gel environmental solvent, stable gel colors and xerogel colors of calcium alginate (Ca alg.) including photosensitive chlorophyll a (chl.a) were obtained. Ca alg. gel containing leucomalachite green (leuco-M) was made by using the same mixed solvents; after gelation by immersion in mixed solvents or in an acidic solution of various pH values, color development was investigated under ultraviolet irradiation (365 nm). From gel rupture stress measurements, absorption spectral measurements, and an X-ray diffraction study, etc., it was found that such gel-color stability mainly depends on the conformational stability of the host gel.

Intramolecular photodimerization of 2-naphthoates: successful application of hydrophobic forces in the preparation of large-ring compounds

The fluorescence spectra and photodimerization of polymethylene bis(2-naphthoate)(N – Mn– N) in aqueous organic binary mixed solvents have been studied. Strong intramolecular excimer fluorescence was observed, suggesting that hydrophobic interactions force polymethylene chains to self-coil. Photoirradiation of these solutions resulted in intramolecular dimerization of 2-naphthoate groups to give ring-closure products. The quantum yields for the photodimerization are significantly greater than those in organic solvents. This work provides an example of the application of hydrophobic interactions in expediting the formation of macrocyclic entities.

Effects of fluorine substitution on the solvatochromic behaviour of an iron(II)–cyanide Schiff base complex

The complex [Fe(CN)2(LL)2], in which LL is the diimine Schiff base derived from 2-acetylpyridine and 4-fluoro-3-methylaniline, is, like other dicyanobisdiimineiron(II) complexes, strongly solvatochromic. Wavelengths of its lowest-energy charge-transfer (MLCT) absorption are reported in water and a range of non-aqueous solvents, in several series of binary aqueous solvent mixtures, in micellar systems, in microemulsions and in aqueous salt solutions. The observed shifts are discussed in terms of solvation in the respective media; this complex appears to be a particularly useful probe of solvation and selective solvation.

Autoprotolysis in aqueous organic solvent mixtures

The primary chemical equilibria which define autoprotolysis in aqueous binary solvents have been elucidated and the constants of these equilibria computed for aqueous solvent mixtures of methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2,3-propanetriol, acetonitrile, acetone, tetrahydrofuran, dimethyl sulfoxide, 1,4-dioxane, and formic acid. The values of these constants explain the different behaviors of the diverse binary solvents. From these fundamental constants, the plan value at any solvent composition of any of the binary solvents studied can be accurately computed

Solvent effects on chemical processes. 3. Surface tension of binary aqueous organic solvents

The surface tension of binary solvents is modelled by analogy to solvation effects arising from solvent-solute interactions. Competitive exchange equilibria are postulated between solvent component I (water) and solvent component 2 (organic cosolvent) for solute, which in this case is air; the solvation shell is thus the surface phase. A quantitative relationship is given between surface tension and mole fractions x1 and x2, the model parameters being exchange equilibrium constants K1 and K2. The equation is analyzed, it is applied to literature surface tension data, and it is compared with an earlier model from this laboratory. Curve-fits are very good, and the parameters appear to possess physical significance.